This invention has to do with spar structures and more particularly with spar structures adapted for use as air foils, e.g. as in wind turbines, cooling tower fans, rotor blades, and like devices intended to be mounted from one end in wind force exposed situations. The invention is specifically concerned with spar structures incorporating an integral fitting adapted for mounting composite spar structures on mountings such as rotational hubs, e.g. those used in wind turbines, fans and rotors on a low-cost, efficient and effective basis. The ensuing description will proceed with particular reference to wind turbines as an illustrative context for the invention spar structure.
The modern quest for low-cost, non-polluting energy sources has prompted a review of the oldest, as well as the newest devices for producing energy. Second perhaps only to the use of flowing water, which is presently highly developed in hydroelectric plants, wind motion has intrigued man as an energy source which is nearly ideal in terms of freedom from pollution and which is tantalizingly potentially low in cost. Modern review of known wind turbine technologies has identified a number of areas which can be optimized in wind turbine design for the purpose of making truly competitive, in certain geographic locations, wind turbine energy generation. Among such areas are energy storage systems for occasions when wind availability does not match energy demand, and maximazation of energy production during wind periods through increased efficiencies in the wind turbine generation process itself, and through engineering of wind turbines to be adapted to effectively capture wind energy without destructive response to unusually high wind conditions, such as periodically sweep most geographic locations where wind turbines appear feasible as energy sources.
The present invention focuses on improvements in spar blade structure engineering. While metal and wooden blades have been proposed for wind turbines, the optimum blade would appear to be incorporative a filament and resin composite spar and air foil blade defining afterbody which promises the weathering characteristics, the strength to weight ratio, and the ease of fabrication in many different configurations and sizes, which will make it the structure of choice for future wind turbine design.
Filament and resin composite spars, however, are in need of design improvements at the point of attachment of the spar to the hub of the wind turbine. Such hubs, typically, comprise a shaft having two radially disposed members onto which the spar based blades are attached. Blades may range in size from fifty to two hundred or more feet in length, depending on the other characteristics of the wind energy generator, and accordingly, the blades are subjected to tremendous centrifugal and bending loads as they rotatively respond to ambient winds. The spar attaching structure should provide for rotation of the spar and afterbody blades on their own longitudinal axis for purposed of changing the blade pitch, whereby efficiency of the wind turbine may be improved.